9.1 What is an earthquake?
In this first video on the earthquake unit, you’ll learn what causes an earthquake, how the
movement of lithospheric plates compares to the opening of a stuck door or the
movement of a line of grocery shopping carts, what a slickenslide is, and how foreshocks
and after-shocks are usually found on either side of the main earthquake event.
Chapter Nine: Earthquakes
• 9.1 What is an Earthquake?
• 9.2 Seismic Waves
• 9.3 Measuring Earthquakes
& Learning about Tsunamis
• 9.4 Tsunamis
As you can see, there are four videos in the series. This is the first video – an introduction
to Earthquakes.
9.1 What is an
earthquake?
• An earthquake is a
form of stick-slip
motion.
• Stick-slip motion can
be compared to a
stuck door.
If you think of lithospheric plates as pushing together and becoming stuck – and then
tension and pressure builds up just as when you try to open a door that is jammed. When
the door finally opens, it opens with a jolt. This same thing happens to large lithospheric
plates. Pressure builds up and sections of the plate resist moving until finally they move
with a jolt. This “jolt” is when the earthquake occurs.
9.1 Stick-slip motion
•
Three conditions are needed for stick-slip
motion:
1. Two objects that are touching each other
where at least one of the objects can move.
2. A force, or forces, that will cause the
movement.
3. Friction strong enough to temporarily keep
the movement from starting.
Use the stick-slip door model to identify these conditions.
Lithospheric plates are always in motion. As two plates move in opposite directions, some
sections get stuck. The friction between the two plates is strong enough to temporarily
stop their movement. Pressure from the mantle builds up and eventually, the stuck place
in the crust “gives” and releases its energy through a jolt. We call this “jolt” a “stick-slip”
motion.
9.1 Friction
• Friction is a
resistance to slip
that occurs when
two objects rub
against each
other.
Friction is the resistance to slip that occurs when two objects rub against each other. In
this example, the sock is smooth on the bottom and so will have much less friction on the
floor than the sneaker, which has a rubber tread designed to increase friction. If you
wanted to slide easily across the floor, you would have much better luck in socks than you
would wearing sneakers.
9.1 What causes earthquake?
• An earthquake is the
movement of Earth’s
crust resulting from
the release of builtup potential energy
between two stuck
lithospheric plates.
The stick-slip motion we have been talking about is where two sections of the brittle crust
stick at first and then are released, causing energy to be sent out from the stick-slip site in
the form of earthquake seismic waves.
Here is a close-up of the same graphic. Two lithospheric plates are trying to pass by each
other, one going away from us, and one moving towards us. At the stick-slip site, friction
(let’s call it POTENTIAL ENERGY) builds up until the moving plates are able to over-come
the blockage. At the point when the blockage is released, an earthquake will occur.
9.1 What causes earthquakes
•
The point below the surface where the
rock breaks is called the earthquake
focus.
The FOCUS of an earthquake is the point below the surface where stick-slip motion
occurred. Rocks break and seismic vibrations are released.
9.1 What causes earthquakes
•
As soon as the rock breaks, there is
movement along the broken surface
causing a split in the surface called a
fault.
A fault line, such as the San Andreas Fault in California, represents the area where two
plate boundaries intersect. Fault lines are generally NOT perfectly straight. Sometimes,
they are difficult to locate and are only revealed through the tracking of repeated small
earthquakes.
9.1 The nature of plates
• The seismic waves from an earthquake are
usually strongest at the epicenter, the point on
the surface right above the focus.
The focus is the point below ground where the earthquake occurred. Deep focus
earthquakes can occur at subduction zones as deep as 700 kilometers down. Shallow focus
earthquakes can be less than 50 kilometers below the surface. If a line is extended straight
up to the surface over the focus of the earthquake, we call this the EPICENTER – the point
on the surface right above the focus.
If buildings are located above the focus at the earthquake EPICENTER, much damage can
occur as this is the area of the strongest seismic waves.
9.1 Slickenslides
• The effect of rock
moving against rock
is evidence of plate
boundaries.
• The rock surface
moving to the right is
called slickensides
because it is smooth
and polished.
A SLICKENSLIDE is an area of rock that is smooth and polished and can only occur when
plate boundaries move against each other with a grinding and smoothing action. Typically
this would occur along a transform boundary.
9.1 The nature of plates
• A cracked shell on a
hard-boiled egg is
similar to lithospheric
plates on Earth’s
surface.
Earth’s crust is like the shell of an egg – very thin compared with the rest of the egg. So
earth’s crust is just a thin skin around the planet – quite brittle and easy to crack and
break.
9.1 The nature of plates
• A moving line of
grocery carts is a
better example of a
moving lithospheric
plate.
• Although a plate may
be moving as a single
unit, its boundaries
act like they were
made of many small
sections like the line
of carts.
In this picture a line of grocery carts is being pushed across a parking lot. Just as the
grocery carts jostle and move back and forth in the line, so too do sections of lithospheric
plates move. Although a plate may be moving as a single unit, its boundaries act like they
were made of many small sections, just like the grocery carts in line.
An earthquake in one section of the San Andreas fault can increase the stress and built-up
energy in another section. The added stress can trigger a second earthquake in the new
section.
9.1 When do earthquakes happen?
• The release of built-up potential energy causes
earthquakes.
• An earthquake is a stress reliever for a
lithospheric plate.
• Once a quake occurs, potential energy builds up
again.
The red area in Tennessee, Kentucky, Indiana, Illinois, Missouri, and Arkansas is called the
NEW MADRID FAULT ZONE. This is an ancient plate boundary. Throughout Earth’s history,
lithospheric plates have been torn apart, added to, and joined to other plates. As a result
of this reshaping there are old plate boundaries inside of the plate boundaries we see
today. In 1895 there was a major New Madrid event.
9.1 When do earthquakes happen?
• The second longest
ever recorded
earthquake occurred in
1964 in Alaska and
lasted for four minutes.
• Foreshocks are small
bursts of shaking that
may precede a large
earthquake.
In 1964 Alaska experienced the second largest earthquake ever recorded in the United
States. The pink area on the map slipped seaward up to 66 feet. The earthquake was
preceded by FORESHOCKS, small bursts of shaking.
9.1 When do earthquakes happen?
• Aftershocks are
small tremors that
follow an earthquake,
lasting for hours or
even days after the
earthquake.
Aftershocks are additional small tremors that may last hours or days or months after the
initial earthquake.
9.1 Secret Code
earthquakes
have
foreshocks
and
aftershocks…
aftershocks…
(5 Words) Read from the top DOWN to the bottom.
Try your hand at decoding this secret message. There are five words. Read the message
from the top of the column DOWN to the bottom.
9.2 Pinpointing an Earthquake
This video deals with seismic waves and how you can use 3 pickup stations to determine
the position of an earthquake epicenter.
Chapter Nine: Earthquakes
• 9.1 What is an Earthquake?
• 9.2 Seismic Waves
• 9.3 Measuring Earthquakes
& Learning about Tsunamis
• 9.4 Tsunamis
This is the second video in our four-part series on earthquakes.
9.2 Seismic waves
• Seismic waves that
travel through
Earth’s interior are
called body waves.
• The two main kinds
of body waves are
P-waves and Swaves.
Seismic waves that travel through the earth are called “BODY WAVES.” The two main kinds
are P-waves (called PRIMARY WAVES), which travel faster than other waves. These waves
push and pull on rock as they travel. The rock moves in the same direction that the wave
moves. The second main kind of waves are S-waves (called SECONDARY WAVES). These
travel more slowly and cause the rock to move in a side-to-side motion.
9.2 Seismic waves
• Seismic waves bend
when they contact
different materials.
• Liquid—like the liquid outer core of Earth—acts
as a barrier to S-waves.
• P-waves pass through liquid.
• Waves on the surface, or body waves that reach
the surface, are called surface waves.
Because of different materials inside the Earth, seismic waves may be bent and even
deflected. Seismic waves can also change speeds by moving faster in cooler material and
slower in hotter material. The liquid outer core blocks S-waves, while P-waves pass right
through. Some seismic waves travel along the surface, and are called SURFACE WAVES.
9.2 Measuring seismic waves
• People who record and interpret seismic
waves are called seismologists.
• Seismic waves are recorded and
measured by an instrument called a
seismograph.
A scientist who records and interprets seismic waves is called a SEISMOLOGIST.
Seismologists study the interior of our planet by observing the way seismic waves travel
through Earth. This process is similar to using X rays to create a CAT scan of the interior of
the human body. The instrument that records the waves is called a SEISMOGRAPH.
Seismographs can be used to study earthquakes along fault zones. From their readings
scientists can determine the strength of an earthquake, how far away it was, and, if they
have data from at least two other stations, the location of the epicenter of the earthquake.
9.2 Measuring seismic waves
• After an earthquake
occurs, the first seismic
waves recorded will be
P-waves.
• S-waves are recorded
next, followed by the
surface waves.
After an earthquake occurs, the first seismic waves recorded by a seismograph will be Pwaves (called PRIMARY WAVES). These waves travel the fastest in a push-pull fashion.
Next, S-waves (called SECONDARY WAVES) arrive, followed by the slowest of all – SURFACE
WAVES.
9.2 Measuring seismic waves
• In a quarter-mile race,
the track is so short
that fast and slow cars
are often just fractions
of a second apart.
• In a long race, like the
Indianapolis 500, the
cars might be minutes
apart.
• The time difference
between slow and fast
cars is related to the
length of the race track.
As in this race car example, if the earthquake is close by, the difference between the arrival
times of P-waves and S-waves will be very small. The further away the earthquake occurs,
the farther apart the arrival time will be between the beginning of P-waves and the
beginning of S-waves.
9.2 Measuring seismic waves
• Seismic waves radiate
from the focus after the
earthquake.
• Three seismic stations
can accurately
determine the times of
body wave arrival.
Seismic waves radiate out from the earthquake epicenter in a circular fashion. Seismic
stations located at points A, B, and C will pick up the seismic vibrations at different times
because they are different distances from the epicenter. Using data from each of the three
stations, it is possible to plot the exact epicenter of the earthquake.
9.2 Distance to epicenter
• Seismologists use
computers to
determine the
distance to an
epicenter.
A seismologist would begin with readings from three different pick-up stations. As you can
see for stations 1, 2, and 3 --- the difference in arrival times between P an S waves varies –
yielding different distances to the epicenter.
9.2 Distance to epicenter
1. Identify three seismic stations and locate them on a map.
2. Determine the time difference between the arrival of the
S-waves and the P-waves at each station (Use chart
data).
3. Convert the time differences into distances to the
epicenter (Use graph).
4. Set a geometric compass so that the space between the
point and pencil on the compass is proportional to the
distances that you found in Step 3. (Use graph scale)
5. Draw a circle around each seismic station location.
6. The intersection of the 3 circles is the epicenter!
In class we will do a lab using these steps to locate an earthquake epicenter. We’ll start
with readings from three seismographs to determine the time difference between the
arrival of S-waves and P-waves. From this time difference you will be able to use a graph to
determine how far away from the epicenter the pick-up station was. Finally, using a
geometric compass you’ll be able to draw concentric circles around the seismic station.
Where the three circles intersect is the location of the earthquake epicenter.
9.2 Distance to epicenter
A graph is used to plot S-P wave differences versus distances to the epicenter. For instance,
a time difference of 30 seconds yields a distance of 250 kilometers. A time difference of 60
seconds yields a distance of 500 kilometers.
Once these distances are calculated, a compass can be used to draw three circles on a
map. Where the circles intersect is where the earthquake epicenter is located.
9.2 Secret Code
TO
YOU
FIND
NEED
AN
THREE
EARTHQUAKE
SEISMIC
EPICENTER
STATIONS
Read DOWN the first column, and then DOWN the second column. (10 words)
Now that you have learned how to plot the epicenter of an earthquake, you are ready for
our EPICENTER LAB and… this secret code. There are ten words. Read DOWN the first
column and then again, DOWN the second column to figure out the message. Good luck!
9.3 Measuring an Earthquake
Once data on an earthquake is recorded, scientists use different scales to rate the intensity
of the event.
Chapter Nine: Earthquakes
• 9.1 What is an Earthquake?
• 9.2 Seismic Waves
• 9.3 Measuring Earthquakes
& Learning about Tsunamis
• 9.4 Tsunamis
This is video number 3 in our four part series on earthquakes.
9.3 Measuring Earthquakes
•
The Richter scale rates earthquakes
according to the size of the seismic waves
recorded on a seismograph.
The Richter scale rates earthquakes according to the size of the seismic waves recorded on
the seismograph. Seismic wave energy increases 10 times for each Richter number change.
This means that a magnitude 9 earthquake on the Richter scale would be 1,000 times more
powerful than a magnitude 6 earthquake. The Richter scale assumes that the
measurements were taken near the earthquake center. A close relative of the Richter scale
is the MOMENT MAGNITUDE scale. These two scales are the same up to level 5. For larger
earthquakes, however, seismologists tend to use the more descriptive Moment Magnitude
scale since it rates the total energy released by an earthquake.
9.3 Measuring Earthquakes
• The largest earthquake recorded occurred
in Chile in 1960.
• It was off the Richter scale; seismologists
estimated this quake to be 9.5.
The largest earthquake recorded occurred in Chile in 1960. It was off the Richter scale at an
approximate 9.5 level.
9.3 Measuring damage
• The Mercalli Intensity
scale has 12
descriptive categories.
• Each category is a
rating of the damage
suffered by buildings,
the ground, and
people.
The Mercalli Intensity scale has 12 descriptive categories. Each category is a rating of the
damage suffered by buildings, the ground, and people.
Because earthquake damage can be different from place to place, a single earthquake may
have different Mercalli numbers depending on how far away the seismic station is from the
earthquake’s epicenter.
9.3 Where do earthquakes occur?
• Earthquakes commonly
occur at the boundaries
of lithospheric plates.
• This is because plate
boundaries tend to be
zones of seismic activity.
Earthquakes commonly occur at the boundaries of lithospheric plates and less commonly
at faults that are inside plate boundaries. Plate boundaries tend to be ZONES of seismic
activity. Therefore, earthquakes do not just occur along neat lines showing the general
plate boundary. The California coast lies along the San Andreas Fault. Many branches of
the fault form a large EARTHQUAKE ZONE.
With both convergent and divergent boundaries, earthquakes signal the build up of
potential energy and its release as plates move towards and away from each other. As
seismic stations pick up earthquakes a fairly accurate plate boundary map can be
constructed over time which clearly shows the size and positions of the major tectonic
plates.
9.3 Earthquakes
•
•
•
Soil types can affect
the amount of
damage caused by
earthquakes.
When seismic waves
pass through the
ground, the soil can
act as a liquid.
This is called
liquefaction.
Soil types can affect the amount of damage caused by earthquakes. When seismic waves
pass through the ground, the soil can act as a liquid. This is called LIQUIFACTION. The 1989
Loma Prieta earthquake caused a lot of damage in San Francisco. The area most damaged
had been built on top of San Francisco Bay mud. Liquefaction occurs when soil is saturated
with water. An earthquake increases pressure on the soil so that the particles separate
with water between them. The result is that the soil acts like a liquid and any building on
the surface will begin to sink, just as if it were sinking in water.
9.3 Earthquakes – Building Materials
• Earthquake vibrations
easily damage heavy,
brittle building materials
like brick, mortar, and
adobe.
• Buildings with welldesigned steel supports
are less likely to be
damaged during quakes.
It is the vibrations caused by seismic waves that results in the most damage in earthquake
areas. Brick, mortar, and adobe construction tends to suffer the most. Steel-reinforced
buildings are more earthquake resistant.
9.3 Earthquakes – Buildings
•
•
•
Mexico City had short, medium, and tall
buildings before an earthquake struck in 1985.
Many of the medium-height buildings were
destroyed.
Why did short and tall buildings survive?
Taller buildings should be more susceptible to earthquake damage – but, this is not always
the case. In the Mexico City earthquake of 1985, it was the medium-sized buildings that
were destroyed. The swaying of the medium-sized buildings happened to match the
earthquake vibrations.
9.3 Earthquakes – Vibrations
•
•
The swaying of the
medium-height
buildings happened to
match the earthquake
vibrations.
This is similar to how
you can make someone
go higher on a swing if
you push them at the
right time.
This made the Mexico City medium-sized buildings sway more and more with each seismic
push of the earthquake. This is similar to how you can make someone go higher and higher
on a swing if you give them a push each time they swing back towards you.
9.3 Earthquakes – 7 Steps to Safety
1. Secure it
2. Plan
5. Drop, Cover, Hold on
3. Disaster Kit
6. Check it out
4. Safety Check
7. Communicate & Recover
Here are 7 steps to Earthquake Safety:
Step 1: Secure it. Conduct a "hazard hunt" to help identify and fix things such as unsecured televisions,
computers, bookcases, furniture, unstrapped water heaters, etc. Securing these items now will help to
protect you tomorrow.
Step 2: Make a plan
Make sure that your emergency plan includes evacuation and reunion plans; your out-of-state contact
person's name and number; the location of your emergency supplies and other pertinent information. By
planning now, you will be ready for the next emergency.
Step 3: Make disaster kits
Your disaster supplies kits should include food, water, flashlights, portable radios, batteries, a first aid kit,
cash, extra medications, a whistle, fire extinguisher, etc.
Step 4: Safety Check
Most houses are not as safe as they could be. There are things that you can do to improve the structural
integrity of your home. Some of the things that you might consider checking include inadequate foundations,
unbraced cripple walls, soft first stories, unreinforced masonry and vulnerable pipes. Consult a contractor or
engineer to help you identify your building's weaknesses and begin to fix them now.
Step 5: DROP, COVER, and HOLD ON!
During earthquakes, drop to the floor, take cover under a sturdy desk or table, and hold on to it firmly. Be
prepared to move with it until the shaking stops.
Step 6: Check it out!
One of the first things you should do following a major disaster is to check for injuries and damages that need
immediate attention. You should be able to administer first aid and to identify hazards such as damaged gas,
water, sewage and electrical lines. Be prepared to report damage to city or county government.
Step 7: Communicate and recover!
Turn on your portable radio for information and safety advisories. Communicate with friends and relatives to
let them know that you are safe.
9.3 Earthquakes -- Response
Learn what to do during an earthquake --- drop to the floor, take cover under a sturdy desk
or table, and hold on to it firmly. Be prepared to move with it until the shaking stops. After
the shaking stops, exit the building and head for an agreed upon meeting place outside.
9.3 Secret Code
WHEN
DROP
AN
COVER
EARTHQUAKE
HOLD
HAPPENS
ON
(8 WORDS)
Read DOWN the left column and then DOWN the right column.
The secret code has 8 words. Start on the left column and read DOWN, then read the right
column DOWN from the top. Good luck!
9.4 Tsunamis
A tsunami is a series of ocean waves that sends surges of water, sometimes reaching
heights of 100 feet onto land. These surges of water can cause widespread destruction
when they crash ashore.
Chapter Nine: Earthquakes
• 9.1 What is an Earthquake?
• 9.2 Seismic Waves
• 9.3 Measuring Earthquakes
& Learning about Tsunamis
• 9.4 Tsunamis
This is the 4th and final video in our series on earthquakes.
9.4 Tsunamis – “Harbor Wave”
• Tsunami is a Japanese word that
means “harbor wave.”
• Sudden movements of the sea floor
cause tsunamis.
Tsunami is a Japanese word that means “harbor wave.” Sudden movements of the sea
floor cause tsunamis. These movements may be earthquakes, volcanic eruptions,
landslides on a steep underwater face, or even a meteor impact. You have learned that
earthquake energy is spread by seismic waves. In a similar way, energy from underwater
movements is sent out as waves on the ocean surface.
9.4 Tsunamis – Cross Section
In the open ocean, wind-driven waves and tsunamis are about the same height. But the
wavelength of a tsunami is much longer than the wavelength of a wind-driven wave. The
wavelength of a wind-driven wave may measure 20-40 meters from crest to crest. It may
take ten seconds or so for a wind-driven wave to pass by. The wavelength of a tsunami is
hundreds of kilometers long! If a tsunami approached your ship at sea, it would cause the
ship to rise gently, less than 10 feet perhaps and then settle gently back after several
minutes. When the tsunami approaches land, the lower front edge of the wave begins to
drag on the shallow bottom. As the front slows, the back of the wave catches up. This
shortens the wavelength. Shortening the wavelength makes the wave crest higher. It’s this
huge crest of water, between 10 and 100 meters high, that comes flowing over beaches
and harbors and can flow up to five miles inland.
9.4 Tsunamis – Sumatra, 2004
On December 26, 2004 monstrous tsunami waves struck the coasts of Sumatra island,
Bangladesh, India, Malaysia, Myanmar, Thailand, Singapore, Maldives, and other territories
bordering the Indian Ocean, affecting 14 countries in total. During the Indian Ocean
earthquake, 1,200 kilometers (750 miles) of the plate boundary slipped when the Indian
Plate slid under the Burma Plate (part of the Eruasian Plate). The seabed rose over 6 feet,
causing huge tsunami waves.
9.4 Tsunamis – Sumatra, 2004
The tsunami was triggered by a very powerful magnitude 9.1-9.3 earthquake with an
epicenter off the west coast of Sumatra, Indonesia. The tsunami and earthquake caused
the deaths of 230,000 people. Waves reached 65 to 100 feet in height and swept over and
destroyed the shores of Indonesia, Sri Lanka, and Thailand. The tsunami even traveled as
far as Africa, nearly 8,000 kilometers (5000 miles) from its start. Tsunami waves can travel
up to 500 miles per hour and move up to five miles inland when they reach the shore.
9.4 Tsunamis – Japan, 2011
The massive tsunami generated by the March 2011 earthquake off the coast of
northeastern Japan was a "merging tsunami" — a type of tsunami long thought to exist,
but seen in 2011 for the first time. In this picture you can see the huge volume of water
that overflows the sea wall in this Japanese harbor. So much water came into the harbor
that boats were carried right over the sea wall into flooded city streets.
9.4 Tsunamis – Japan, 2011
The magnitude-9.0 Tohoku-Oki temblor, the fifth-most powerful quake ever recorded,
triggered a tsunami that doubled in intensity over rugged ocean ridges, amplifying its
destructive power at landfall. The fronts merged to form a single, double-high wave far out
at sea. With the on-rushing height of the wave at 30 to 100 feet higher than normal,
Tsunami waves easily swept aside entire buildings and towns as they moved inland.
9.4 Tsunamis – Japan, 2011
This wave was capable of traveling long distances without losing power. Ocean ridges and
undersea mountain chains pushed the waves together along certain directions from the
tsunami's origin. The NASA Jason-1 satellite passed over the tsunami on March 11, as did
two other satellites — the NASA-European Jason-2 and the European Space Agency's
EnviSAT. All three satellites carry radar altimeters, which measure sea-level changes to an
accuracy of a few centimeters. Each satellite crossed the tsunami at a different location,
measuring the wave fronts as they occurred. Researchers think ridges and undersea
mountain chains on the ocean floor deflected parts of the initial tsunami wave away from
each other to form independent jets shooting off in different directions, each with its own
wave front.
9.4 Tsunami – Detection Buoy
We now have a series of tsunami detection buoys that ring the Pacific Ocean. A recorder
on the sea floor monitors changes in water pressure. These stationary monitors can detect
tsunamis as small as 1 centimeter. The seabed monitor then relays its information to a
floating buoy on the surface which transmits its data to a satellite, which then relays it to a
ground station.
9.4 Tsunami – Detection Buoy Network
Tsunami detection buoys have been placed along the coasts of Pacific Plate continents to
try to give nations advance warning of approaching tsunamis. Since the Sumatra
earthquake of 2004, additional buoys have been placed in the Indian Ocean area to give
those nations coverage as well. The Pacific Tsunami Warning System is based in Honolulu,
Hawaii. It monitors Pacific Ocean seismic activity. A sufficiently large earthquake
magnitude and other information triggers a tsunami warning.
9.4 Tsunamis – In Case of …..
• RUN to
higher
ground!
• Do not
wait, do not
investigate,
RUN!
A tsunami’s trough, the low point beneath the wave’s crest, often reaches shore first.
When it does, it produces a vacuum effect that sucks coastal water out to sea and exposes
the harbor bottom and sea floor. This is called DRAWBACK. This retreating of sea water is
an important warning sign of a tsunami, because the wave’s crest and its enormous
volume of water typically hit shore five minutes or so later. Recognizing this phenomenon
can save lives. So, if you see the water draw back from the beach – RUN to higher ground.
A tsunami is usually composed of a series of waves, called a WAVE TRAIN, so its destructive
force may be compounded as successive waves reach the beach. People experiencing a
tsunami should remember that the danger may not have passed with the first wave and
should wait until official word is given that it is safe to return to vulnerable locations.
9.4 Secret Code
in
case
of
a
tsunami
run
to
higher
ground
(9 Words) Read DOWN the left column, then DOWN the right column.
Now that you know all about tsunamis, try your hand at this secret code. There are 9
words. Read DOWN the first column and then DOWN the second column. Good luck!